Task configuration

The PROFINET controller protocol must always be linked to a task. The protocol is also processed with the set task time. Theoretically, the controller can also be processed via a PLC or NC task, for example. However, if a PLC project is stopped (e.g. due to a restart or debugging), the PROFINET part is also stopped. To avoid such a side effect, it is advisable to always create a free-running SyncTask.

Fig.25: Sync Task tab

Make sure that the task cycle is in a PROFINET cycle. This means that the basic cycle for PROFINET is 31.25 µs. This cycle is then always multiplied by the SendClockFactor (SCF) to obtain the basic cycle. The SendClockFactor is usually set to 32 for RTClass1. This is also the minimum PN cycle for RTClass1 for the Beckhoff PROFINET controller and results in the smallest cycle time of 1 ms. Further reductions take place using a ReductionRatioFactor. This always corresponds to a multiple of the minimum PN cycle. For RTClass1 the smallest cycle must always be doubled (permissible cycle times (for RTC1) with an SCF of 32 are 1, 2, 4, 8, … ,512).

The SCF can and must be reduced in order to achieve faster cycle times for RTClass3 as well. This is presently at least 16 for a Beckhoff IRT controller (EL6632), which corresponds in turn to a basic cycle of 500 µs. If the PROFINET clock is reduced in this way, it must also be ensured that the time of the triggering task is adjusted accordingly.